1. Field of the Invention
This invention relates to facsimile receivers. More particularly, this invention relates to receiver imaging arrays having a plurality of energy sources and means for accessing and activating the energy sources.
2. Description of the Prior Art
In a conventional facsimile transceiver, transmission of data is performed by scanning a datacontaining document line by line and by converting the light reflected from the scanned portions of the document into a series of corresponding electrical signals defining successive picture elements (pels) in each line. Those signals are transmitted, typically over a conventional telephone line, to a remote facsimile transceiver where they are processed to reproduce the information on a suitable print medium.
In the receiver portion of a transceiver, several electronic and mechanical techniques are in common use for the purpose of processing received data to produce an image on a print medium. One such technique employs a mechanical stylus, operating in response to the received data signals, which prints the desired pattern on specially prepared paper. Another technique employs a print paper which contains overlaying black and white layers. Portions of the white layer are selectively burned or etched away by means of an electrically charged stylus that operates in accordance with the received data signals.
Still other known facsimile receivers employ a light source, such as a cathode ray tube. The light beam is modulated in accordance with the received data signals and is scanned over a suitably treated medium to form a pattern of locations on the paper. The medium may be photographic film which is subsequently processed to produce a permanent image. U.S. Pat. No. 3,924,061 issued to Tregay et al on Dec. 2, 1975, and U.S. Pat. No. 3,869,569 issued to Mason et al on Mar. 4, 1975, are examples of such facsimile receivers.
In yet other receivers, the light source employed is a laser beam. Such receivers operate in a manner similar to the manner of those receivers employing a cathode ray tube, but the beam is generally applied to a print medium other than photographic film. In "an experimental Page Facsimile System," by H. A. Watson, Bell Laboratories Record, March 1975, page 153, a laser receiver is described where the print medium is bismuth film.
A common thread to the above described techniques is the use of a single light source to form a two dimensional received image and the use of analog modulation of the light source intensity to control the gray levels of the resultant pattern.
In a slightly different field of art, a two-dimensional display is achieved by the use of a plurality of light sources arranged in a matrix configuration. Of common knowledge are gaseous displays and light emitting diode (LED) arrays which are used extensively to display alphanumerics. For example, LED arrays having groups of diodes preselectively interconnected and activated as a group are commonly used in calculator displays. A slightly different LED array arrangement is disclosed in U.S. Pat. No. 3,800,177 issued to Russ on May 26, 1974, where the LED array is arranged in a horizontal and vertical address matrix and where the activation of a particular horizontal and vertical address line pair activates a single LED. Whatever the application, LED arrays have heretofore been used only to display a two-tone image (generally red on a black background).
Different arrangements, such as described in U.S. Pat. No. 3,863,023 issued to Schmersal et al on Jan. 28, 1975, provide multitone displays. In the arrangement described by Schmersal, multitone operation (graduated intensity levels of a particular tone such as green, red, black, etc.) is achieved in a gaseous discharge panel having a multiple number of memory planes. In particular, a number of gray level ranges are defined and an equal number of memory planes are employed, with each memory plane having the same number of storage areas as the number of storage and discharge areas in the display panel. (For simplicity, the term "gray level" is employed in this disclosure regardless of the actual hue employed).
The Schmersal et al apparatus is cumbersome because it requires the use of hardware that is both bulky and expensive. Additionally, the memory planes of Schmersal must be accurately aligned, and separately driven with high voltages.
Another method for effecting different gray levels is described in U.S. Pat. No. 3,604,846 issued to Behane et al on Sept. 14, 1971. In accordance with the teachings of Behane et al, grey level graduations can be achieved by subdividing the area of each picture element (pel) into a plurality of subareas, e.g., a 3 .times. 3 matrix having nine subareas, and by marking black a preselected number of the subareas in accordance with the gray level desired. Thus, white pels are obtained by marking black none of the subareas, progressively darker gray pels are obtained by marking black greater numbers of subareas, and black pels are obtained by marking black all nine subareas.
This method is useful in situations where high receiver resolution is inherent in the system and is, therefore, obtained at low cost. Where high resolution is not inexpensively available, this method becomes too costly because for each microscopic resolution element (pel), a large plurality of microscopic resolution elements (the subareas) must be employed.
The alignment, resolution, and expense drawbacks of prior art multitone receivers have, to a large extent, been eliminated by a facsimile receiver system disclosed in my copending applications Ser. Nos. 750,273 and 750,275 filed on Dec. 13, 1976. In those systems, received signals are stored in a multiport memory, wherefrom they are simultaneously applied to a display array composed of energy sources, such as LEDs. Time duration controlled pulses are applied to activate the LEDs, causing them to light up in accordance with the data stored in the multiport memory.
The newly disclosed facsimile systems can operate at very high data rates because they simultaneously activate all of the energy sources. However, in applications where the received facsimile data rate is low, the complexity associated with simultaneous activation of the energy sources is not warranted. Since the pel data is received at a low rate, there is sufficient time between receptions to illuminate each received pel as it arrives.